Electrical transmission of messages



Feb. 27, 1945.

C. W. HANSELL ELECTRICAL TRANSMISSION OF MESSAGES Filed Dec. 18, 1940 3 She ets-S heet 1 INVENTOR- b- 27, 1945- c. w. HANSELL 2,370,160

ELECTRICAL TRANSMISSION OF MESSAGES Filed Dec. 18,- 1940 s Sheets- Sheet 2 AW 1 QWQQA P Feb. 27, 1945. Q w, LL 2,370,160

, ELECTRICAL IRANSMISSION OF MESSAGES Filed Dec. 18, 1940 3 Sheets-Sheet 3 INVE TOR ATTORNEY Patented Feb. 2 7, 1945 v j ELECTRICAL TRANSMISSION or MESSAGES Clarence W. Hansel], Port Jeflerson, N. 2., assignor to Radio Corporation of America, a corporation of Delaware Application December 18, 19 10, Serial No. 370,579

6 Claims.

Thepresent invention relates to the transmission of messages by wire and/or radio, and particularly to improvements in multiplex systems.

It is known to provide a multiplex facsimilesystem for the transmission of messages and vidually associated therewith a source of o scillations of a particular frequency, preferably an audio frequency, whereby the current through each scanning element is varied, in the case of the brush, in dependence upon contacting the electrically conductive letters, or in the case of the photocell, in dependence upon the intensity of the light reflected from the message characters. My United States Patents Nos.

1,751,584 and 2,143,875, granted respectively a March 25, 1930, and January 17, 1939, are illustrative of such known systems. It is also known to employ a single channel facsimile scanner for the transmission of messages.

Both of the foregoing known types of facsimile systems have certain disadvantages which the system of the present invention is designed to overcome, and certain advantages which the invention utilizes. For example, the multiplex channel system is very desirable over a long distance high frequency radio. circuit because for a given rate of reproduction, the rate of keying or modulation on each channel can be made much less than that required in a single channel system. Also, the use of multiplemng in a manner to permit scanning the whole width of a line of type at once very greatly reduces the requirements for synchronism between scanning elements at the transmitting and receiving terminals so that no elaborate synchronizing equipment of any kind is required. On the other hand, multiplex equipment at the transmitter is cumbersome and unduly multiplied. The present invention combines the simplicity of the scanning" elements in thesingle channel system with the circuit advantages of the multiplexsystem.

Briefly stated, the present invention employs a single photocell scanner at the transmitter whose output is divided by means of a. commutator or its equivalent into a multiplicity of channels, say. tenv ortwelve. In a preferred embodiment, the scanning system utilizes a 1'0- tating mirror, and the commutator is driven synchronously with the mirror and connects one after another of the channels to the photocell or photocell amplifier output as the point of light from the mirror passes fixed lines or positions on the paper tape. Thus each channel is energized for somewhat less than 10% of the time in accordance with the marking along the tape for its particular line. This 10% marking energy is thenmade to last over in each channel fora time of about of each scanning intervaland the final result in each of the ten channel circuits is substantially the-same as if a portion of the tape were continuously scanned by ten different photocells. Thus, the outi put of the single channel facsimile scanner might be split up into ten or twelve channels with time elongation in each channel, the energies in the ten or twelve channels conveyed to a multiple phase, frequency, single side band or amplitude modulated transmitter, from wnich the message 1 waves are radiated, then received, separated and recorded on a multiplex facsimile recorder or its equivalent.

Advantages of the present invention are: (1) Greater speed of transmission is obtained. I can operate the system at four to ten times the speed of the normal single scanner system without exceeding the limitations 'of recording,

by carbon paper or typewriter ribbon. (2) The signalling channels may be operated at slow speeds relative to the speed which would be re-,

quired for single channel use, thus reducing the distortion efiects produced by multipatn pnenomenon in radio circuits. (3) No synchronism is required between transmitting and rece1v-' or squeezing together of the letters on the tape,

but in either case the letters are legible. And (4), the amount of equipment at the transmitter is reduced over what would otherwise be required in a multi-channel system.

A better understanding of the invention may be had by referring to the following description which is accompanied by drawings, wherein: Figs. 1 and 3 illustrate two diiler'ent embodi ments of facsimile transmitter circuits embodying the principles of the present invention Fig. 2 is a fragmentary view or a portion of the tape used in the transmitter circu'iLand is although all use a common principle underlying the invention.

In Fig. 1 there is shown a facsimile transmitting system in accordance with the invention, employing a single photocell l for scanning purposes, whose output after being amplified by amplifier 2 is divided into twelve channels by means of a distributor or commutator 3. This distributor is shown in its simplified form as comprising a rotating brush 4 which is designed to sweep over and contact in succession twelve segments, each of which is connected to a vacuum tube keyer 5. The outputs from the vacuum tube keyers 5, 5 are coupled through audio frequency transformers 6 to a common transmission line TL, the latter extending to a suitable radio transmitter T of the amplitude, phase, frequency or single side band type. The output from radio transmitter 1 passes over a transmission line 28 to a suitable antenna 8. Associated with each vacuum tube keyer 5 is an audio frequency tone oscillator, there being a different audio frequency oscillator for each channel. These tone oscillators have been labeled f, f1, f2, in order to designate the different audio frequencies. In

practice, all audio frequency tones for all twelve channels may be supplied from a single multitone generator of any well known form and the same generator may be in simultaneous use on other circuits. It should be noted that the oscillators 1, f1, f2, etc., supply their tones to the grids of the vacuum tube keyers through audio frequenc transformers 9, 9. In circuit with the grid of each vacuum tube keyer, there is provided a condenser l0 and a resistor II to supply a suitable time delay which allows applied charges from the photocell amplifier 2 to leak off the condensers very slowly. Rectifiers I2 and I3 serve, respectively, to supply negative and positive potentials to the grid and anode electrodes of the vacuum tube keyers. time that only three of the distributor or commutator segments and their associated vacuum tube keyers 5, ,5 have been shown connected through a complete ,circuit to the radio transmitter I. The other segments connect with their associated keyers 5, 5 and with transmission line .TL in the same fashion, but the complete circuit connections have not been shown for the sake of simplifying the drawings.

The tape to be scanned is indicated at M. This tape is shown arranged around a roller or drum I5 which serves to continuously advance the tape during the scanning of the letters on the tape. The message to be transmitted may be typed on the tape and is here shown by way of example It should be noted at this shown in the drawings, a flying spot of light (identified as 20 in Fig. 2) will play upon the line of type to be scanned at the left edge of the tape. The angle of incidence of the beam is such as to direct this spot of light 20 on the left hand edge of the letter R, and as the mirror rotates this flying spot of light will move, linearly, transverse to the length of the tape in the direction of the arrow until such time as the flying spot of light reaches the right edge of the tape, when the spot will vanish. The spot vanishes as the facet of the mirror upon which the light impinges moves out of position. At this time another, facet of the mirror will come into position and be adjacent,the lens l8 and the process of scanning a line of the tape will be repeated. Each of the segments of the distributor 3 will be assigned to a chosen position across the width of the tape, so that if there are twelve distributor segments as assumed, there will be twelve positions across the width of the line of type. Thus we may imagine twelve scanning lines across the tape 14, as indicated by the twelve vertical lines on the tape of Fig. 2, the positions corresponding to the distributor segments being numbered 1 to 12. The output of the photocell l which receives the light reflected from the tape 84 and is controlled by the marking of the letters along the lines on the tape is applied through the distributor to the twelve different circuit channels. Thus, each of the twelve circuits or channels associated with the distributor segments is energized for something less than one-twelfth of the total time required to scan a line of type from left to right on the tape. The energization of each channel occurs at a rate corresponding to the scanning speed and with an intensity corresponding to the marking on the tape. The rotating mirror IS, the distributor 3 and the drum l5 are synchronized relative to each other by means ofa gear train 2i which, in turn, is driven by a suitable motor 22. The brush 4 on the commutator rotates in synchronism with the rotating mirror and makes one complete revolution for each facet or side of the mirror so that if asix facet mirror is employed, the brush 4 will rotate six times for each complete revolution of the mirror. For each passage of the light spot 20 across the tape L4, the tape is arranged to advance a distance equal to a fraction of the diameter of the spot. The drum I5 is arranged'to move continuousl and not intermittently.

As mentioned above, there is associated with each channel a suitable time delay circuit comprising a resistance H and a condenser III. This delay circuit will allow the applied charge on the condenser [0 to leak off slowly, so that each of "the twelve channels may give a substantially as comprising the letters R C A. For scanning the tape, there is provided a suitable light source l6 which throws a beam of light through a disc I! having a suitable hole or slot therein and through a condensing lens, I8 upon a multifacet rotating mirror is. The light which im-. pinges upon the facet or side of the rotating mirror which happens at the moment to be facing the lens l8 will scan the tape across a width of a steady output even though an input is periodic and lasts less than one-twelfth of the total time. In other words, the condenser 10 provides a. time delay so that the charge on the condenser permits the vacuum tube keyer 5 to continue passing current for some time after the brush on the commutator has passed oil the associated segment. In thisway the tone output for each channel is not modulated at the scanning rate.

When the facet of the mirror which- The condenser III has a relatively long time dela so that all potential changes on the grid of the keyer are normally determined by the po-' tentials applied from the commutator. After a charge is placed on the grid, the condenser will maintain this charge until the charge is changed by connection to amplifier 2 through the commutator. As a safety measure, in case motor 22 should stop for some reason, or amplifier 2 should fail, the rectifier l2 through resistances II will bias tubes 5 to cut-off after a time delay long compared with one revolution ohcommutator 3. The mirror i9 is designed to rotate at a much faster rate than thecharge leaks off the condenser I0. Thus by making the scanning rate high enough compared with the motion of the Then, if the receiving scanner is run fast enough compared with th movement of the tape, a satisfactory .record will be made. In practice, it

. might be desirable'to give the vibrator one pulse tape l4 over the drum I5, there is obtained an output from all the keyers 5, 5 which is equivalent to a complex wave representing the sum of the waves of frequencies f, f1, f2, etc, at any instant, depending upon the number of channels which are energized by the configuration of the letter at that one instant, which complex wave is transferred over line TL through suitable audio amplification .(not shown) to the radio transmitter l, and then through a land line 28 leading fromothe transmitter to the antenna 8. It will be obvious that when all the keyers are passing current, the complex wave sent out over the antenna will contain all the twelves tone components corresponding to the oscillations produced by the twelve oscillators 1, f1, f2

fii.

The system may be so designed that for an all white tape the keyers 5, 5 either pass or cut off for each passage of the scanner across the recurrent, depending upon the polarity of the transmission desired; while for an all black tape,"

the keyersjwill function oppositely. Although a single tube type keyer 5 has been shown for each channel, such a keyer can be replaced by a pushpull keyer wherein the control potentials from the commutator is push-push to the grids of the keyer while th audio tone is push-pull to the grids and output is taken in push-pull.

That portion of the transmitting system of Fig. 1 which includes the transmission line TL and the radio transmitter! and the antenna 8 may, if desired, be similar to the correspondingly arranged elements shown in Fig. 8 of my Patent 1,751,584, or Fig. 1 of my Patent 2,143,875,-

supra. The transmitter I may, desired, be a single side band radio transmitter and also, if

' desired, an amplitude, phase or frequency modulated transmitter, depending upon the elements which precede the transmitter. It may also be replaced by a wire line circuit for wire line communication systems. m

For receiving th signals sent out over the system of Fig. 1, any suitable arrangement may be employed wherein the audio frequencies characteristic of the'various channels are reproduced and filtered out to record the signals at a suitable scanning head. A receiver which can be used where photographic recording is desired is shown in Fig. 11 of my Patent 1,751,584, supra; or in the case where mechanical recording is desired, there may be employed ;a receiver of the type shown .in Fig. 3 of my-United States Patent 2,143,875.

Where electric chemical recordingis desired, each tone can be filtered out in the receiver as in Fig. 11 of my Patent 1,751,584, then rectified and the rectified current appliedto a finger or contact engaging a chemically treated papen By aligning the twelve fingers corresponding to the twelve channels on thetreated paper in the re-' cycles, etc.

only for each line crossed, so that the vibrator to reproduce solid black would strike twelve places on the recording ribbon or carbon paper scans the tape passing over the drum. The

recorder includes an electromagnetically actuated recorder bar 33 whose energizing coils are excited through an audio transformer 35 by a source of alternating current 34. The recording is done by hammering the paper and typewriter ribbon between the spiral 32 and the recorder vibrator bar 33. r

Fig. 3 is a modification of the system of Fig. 1, showing how the potentials delivered by the commutator 4 can cause a change in the frequency of the tone source instead of a'change in amplitude. In effect, Fig. 3 shows the principles of' the invention applied to a subcarrier frequency modulation'system. Element 23 corresponds to any suitable frequency modulator which is responsive to potential variations. Osci1lator 24, 24' or 24" in the output of the frequency modulator is adjusted for a suitable audio frequency range, there being different audio frequency ranges for the different oscillators. *As an illustration, oscillator 24 may cover a range from 400 cycles to 475 cycles; oscillator 24' may cover a range from 500 cycles to 575 cycles; while oscillator 24" may cover a range from 600130 675 Since the other elements of Fig. 3 are substantially identical with those shown in Fig. 1, the same numerals have been applied to designate the same parts.

Fig. 4 illustrates a receiving arrangement to which the principles of the present invention may be applied. The receiving system of this figure is totally independent of the transmitters employed in Figs. 1 and 2, and is primarily designed for a single channel transmitter of the known type. In Fig. 4 there is shown an arrangement for dividingthe received signal coming from a single channel-into a multiplicity of difierent circuits. For this purpose, there is employed a distributor 3' having a brush 4' which separates the signals received in 25 intotwelve diflerent channels. The receiving system 25 includes all means necessary for holding the distributor? in synchronism with the transmitting scanner. Each segment on the distributor 3' associated with a contacting brush arrangement .26 bearing on a chemically treated tape l4 advancing over a metalroller l5. Suitable condensers 21 serve to hold the potential'on each scanning point between the revolutions of the commutator 3. The potentials placed on the condenser 21 are determined by the potential on the rotating brush 4' of the commutator at the time of contact with the associated segments.

What is claimed is:

1. In a facsimile communication system, a transmitting terminal including a relatively high speed scanner containing only one light translatingelement, a receiving terminal, a transmission medium between said transmitting and receivmaintain a continuous output in the absence of a change of polarity applied thereto, means for combining the outputs of said keyers and for modulating a carrier in accordance with the resultant energy, and rectifier means for biasing said keyers to cut-off in the event of failure of ing terminals, a recording reproducing system at said receiving terminal, and a rotary distributor at said receiving terminal for dividing the received signals into a plurality of channels corresponding to assigned segments on said distributor prior to impressing said signals upon said recording reproducing system.

2. A system in accordance with claim 1, char-.

acterized in this that said reproducing, system includes a continuously advancing chemically treated paper and a plurality of contact. pins engaging said paper, each of said pins being associated with a channel.

3. In a facsimile communication system, a transmitting terminal including a continuously advancing tape having message characters thereon, a scanner including a source of light rays and a rotating mirror for scanning said characters line by line and a single light translating element upon which said rays of light impinge,

through said distributor for controlling the passage therethrough of the tone in said channel,

means for combining the outputs of said keyers,

:and a common rectifier supplying to the grids of said electron discharge device keyers a negative bias of a sufficient magnitude to cut off said keyers in, the event of failure of said distributor but only after a time interval which is long compared with one revolution of said distributor.

4. In a facsimile communication system, a transmitting terminal including a continuously advancing tape having message characters thereon, a scanner including a source of light rays and a rotating mirror for scanning said characters line by line and a single light translating element upon which said rays of light impinge, an amplifier for said light translating element, a distributor for dividing the output of said eminent into a plurality of channels corresponding to assigned portions of said line, whereby each channel is energized with an intensity varying in accorda'nce with the light reflecting character hr the assigned portion of the scanning line, sources of diflerent tone frequencies in circuit ith said channels, an electron discharge device keyer associated with each channel and responsive te, potential changes applied thereto by said light: translating element through said distributor for controlling the passage therethrough or the tone in said channel, a time delay network associated I with each keyer for conditioning aid keyer to said amplifier and after a time interval which is long compared with one complete cycle of operation of said distributor.

5. In a facsimile communication system, a transmitting terminal including a continuously advancing tape having message characters thereon, a scanner including a source of light rays and a rotating mirror for scanning said characters line by line, and a single light translating element upon which said rays of light impinge, an amplifier for said light translating element. a distributor for dividing energy representative ofthe output of said element into a plurality of channels each of which is assigned to a predetermined portion of said line, driving means linked to said mirror and to said advancin tape and said distributor for synchronizing the movements thereof, whereby each channel is energized with an intensity varying in accordance with the light reflecting character of the assigned portion of the scanning line, alternating current sources of different frequencies in circuit with said channels, an electron discharge device circuit associated with each channel and responsive to potential changes applied thereto by said light translating element through said distributor for modulating the character of the alternating current energy associated with the same channel, and a utilization circuit connected in common to the outputs of the electron discharge device circuits ofall of said channels, and means in common to said electron discharge device circuits for biasing the same to cut-off in. the event of failure of said distributor or said amplifier.

6. In a facsimile communication system, a transmitting terminal including a continuously advancing tape having thereon the intelligence to be conveyed, a scanner including a source of light rays and a rotating mirror for scanning said intelligence line by line, a single photoelectric cell upon which said rays of light impinge, a rotary distributor for dividing energy representative ,of the output of said cell among a plurality of segments on said distributor, channels assigned to difierent segments of said distributor, driving means linked to said mirror and also to said advancing tape and said distributor for synchronizing the movements thereof, whereby each segment and associated channel is assigned to a predetermined position on the line of intelligence to be scanned, an electron discharge device keying circuit associated with each channel, a common utilization circuit for the outputs of saidkeying circuits, and a time delay circuit associated with each electron discharge device :keying circuit for enabling each channel to supinterval which is long compared with one revolution of said distributor.

CLARENCE W. HAN 

